Method of making a camshaft for reciprocating piston engines

ABSTRACT

Axially spaced cams and bearing rings mounted on a tube are permanently secured to the tube by circumferentially spaced projections on the tube extending into grooves formed on the inside surfaces of the cams and bearing rings.

This is a division of application Ser. No. 819,837 filed Jan. 17, 1986,now U.S. Pat. No. 4,781,076.

.Iadd.BACKGROUND OF THE INVENTION .Iaddend.

This invention relates to camshafts for reciprocating piston engines.More particularly, this invention is a new camshaft and a new method ofmaking a camshaft in which bearings, cams and the like are produced asindividual parts and are fastened to the shaft.

The U.S. Pat. No. 4,382,390, issued May 10, 1983, to Friedrich Jordanand entitled, "Camshaft for Reciprocal Piston Engines", shows a camshaftin which bearings, cams, and the like are produced as individual partsand are fastened to the tube. In the Jordan camshaft, a tube is expandedby hydraulic or rubber means to conform the outside wall of the tubewith the inside surface geometry of the cams and bearing rings. However,a big disadvantage in making the Jordan camshaft is that the wall andthe axis of the tube inside the cams is completely offset from the walland the axis of the rest of the tube. Thus, it is necessary that thecams be inserted into a die which corresponds to their outer shape inorder to be sure that the widening of the hollow shaft will not causesubstantial deformation of the cams.

The camshaft for a reciprocating piston engine and the method of makingsuch a camshaft of this invention does not require that portions of thetube wall be completely offset to an axis different from the axis of therest of the tube. Therefore, the forces necessary to interlock the camsand bearing rings with the tube are far less than the forces required byJordan and usually the specially formed die required by Jordan isunnecessary.

Other current methods for making camshafts in which bearings, cams, andthe like are produced as individual parts and fastened to a tube includeuniformly expanding a tube to interlock with axial splines in the caminside diameter. A uniform internal pressure is applied to expand thetube to uniformly match the outside diameter of the tube with the insidediameter of the cam. At this pressure, the cam is not yet stressed andno tube material has flown into the splines. In order for material toflow into the splines, the internal pressure in the tube must beincreased. At the higher pressure, as the tube material flows into thesplines, the cylindrical inside diameter portion of the cam is stressed.The resulting tensile stresses in the cam inside diameter tend to causecracks if the cam is not in the soft state of heat treatment. Even ifthe cam is in the soft state, the stress situation is undesirable and istypically countered by the application of external pressure on the camequivalent to that of the internal stresses. To apply the externalstressing, some means of pressurization is set-up, such as a die orhydraulic system which always increases costs.

The camshaft for a reciprocating piston engine and the method of makingsuch a camshaft of this invention require much smaller total energy(forces). The stressing of the inside diameters of the cams and bearingsis essentially eliminated. Thus, fully hardened cams and bearings can bereadily attached to the tube at very low cost.

.Iadd.SUMMARY OF THE INVENTION .Iaddend.

Briefly described, the camshaft comprises a rotatable tube having aplurality of circumferentially spaced axially extending projections onits outside surface. The projections are formed by expanding portions ofthe wall of the tube away from the axis of the tube. Axially spaced camsand bearing rings are mounted about the tube. Each cam and each bearingring has circumferentially spaced, axially extending grooves on theirinner surfaces The projections of the tube extend into grooves of thecams and bearing rings to permanently secure the cams and bearing ringson the tube.

Briefly described, the new method of making a camshaft comprises axiallyspacing and placing the cams and bearing rings on the rotatable tube.Each cam and each bearing ring has circumferentially spaced, axiallyextending grooves on their inner surfaces. Portions of the wall of thetube are expanded away from the tube axis and into the grooves on theinner surfaces of the cams and bearing rings.

The invention, as well as its many advantages, may be further understoodby reference to the following detailed description and drawings inwhich:

.Iadd.BRIEF DESCRIPTION OF THE DRAWING FIGURES .Iaddend.

FIG. 1 is a longitudinal section showing the axially spaced cams andbearing ring slipped over the tube;

FIG. 2 is a sectional view taken along lines 2--2 of FIG. 1 and in thedirection of the arrows;

FIG. 3 is a sectional view taken along lines 3--3 of FIG. 1 and in thedirection of the arrows;

FIG. 4 is a longitudinal section through the camshaft showing the partsafter an expander tool has moved partially through the tube to displacelongitudinal portions of the tube;

FIG. 5 is a view taken along lines 5--5 of FIG. 4 and in the directionof the arrows; and

FIG. 6 is a sectional view, on an enlarged scale, showing theinterlocking arrangement of a tube projection into the groove of thecam.

.Iadd.DETAILED DESCRIPTION .Iaddend.

In the various figures, like parts are referred to by like numbers.

Referring to the drawings and more particularly to FIG. 1, themanufacture of the camshaft is accomplished by slipping the cams 10 and12 and bearing rings 14 (only one bearing ring shown) over the tube 13at the desired location. The cams and bearing rings are axially spacedfrom one another and held in position in their desired axial and radialpositions.

The inside surfaces of each cam and the inside surface of the bearingring have inside diameters sufficiently larger than the outside diameterof the tube 13 to provide a tube-to-cam clearance and a tube-to-bearingring clearance ranging from 0.001 inches to 0.010 inches. Thus the camsand the bearing ring may be easily slip fit over the tube.

The inside surface of cam 10 and the inside surface of cam 12 havecircumferentially spaced grooves 22 and 24, respectively, axiallyextending completely through the cams 10 and 12. Similarly, the insidesurface of the bearing ring 14 has circumferentially spaced grooves 26axially extending completely through the bearing ring 14.

To permanently secure the cams and bearing ring on the tube, portions ofthe wall of the tube are expanded away from the tube axis and into thegrooves on the inside surfaces of the cams and bearing ring. In theembodiment shown in FIGS. 4 through 6, the portions of the tube aremechanically expanded.

As shown in FIG. 4 an expander tool 36 is shown after it has been movedpartially through the tube 13. The expander tube 36 has been movedaxially through the bearing ring 14 and the cam 12. Of course, tocompletely make the camshaft, the operation will be completed after theexpander tool 36 has moved through the cam 10. A plurality ofcircumferentially separated semi-spherically shaped hard materialprotrusions 28 are embedded in the expander tool 36 adjacent one end ofthe expander tool 36. The effective diameter of the protrusions 28 issufficiently larger than the inside diameter of the tube 13 to cause theprotrusions to expand portions of the tube 13 into the cam grooves andbearing ring grooves to permanently secure the cams and bearing ring onthe tube.

As shown in FIG. 5, the semi-spherical hard material protrusions 28 arepositioned so that as the protrusions move within the tube past the camor bearing the hard material protrusions 28 will expand the softer tubematerial into the grooves. As a result of the expansion, the entirecircumference of the tube 13 is moved outwardly. Because of the slightdifference between the initial diameter of the tube 13 and the insidesurfaces of the cams and bearing ring, the outside surface of the tubepresses tightly against the inside surfaces of the cams and bearingring.

The completed camshaft for reciprocating piston engines will include therotatable tube 13 with the plurality of circumferentially spaced axiallyextending projections 30 (see FIG. 6) on its outside surface. Theprojections are, of course, formed by expanding portions of the wall ofthe tube away from the axis of the tube. Note that all of those portionsof the wall which are displaced are expanded away from the axis of thetube so that there is no offset or displacement of the tube wall. Thatis, the axis of the cams and the axis of the bearing ring are the sameas the axis of the remainder of the tube 13. This is in sharp contrastto the camshaft shown in the U.S. Pat. No. 4,382,390 issued May 10, 1983to Friedrich Jordan and entitled, "Camshaft For Reciprocal PistonEngines". The projections of the tube extend into the grooves of thecams and bearing to permanently secure the cams and bearing ring on thetube.

As a specific example, the tube 13 may range from 1 inch to 11/4 inchesoutside diameter with a wall thickness ranging from 0.125 inches to0.150 inches, depending on the intended use of the camshaft. Forexample, camshafts for automotive and diesels would be larger than forother purposes. The tube-to-cam clearance and the tube-to-bearing ringclearance .Iadd.ranges from 0.001 inches to 0.010 inches. The grooves inthe .Iaddend.cams and the grooves in the bearing ring may beapproximately 0.020 inches deep with a radius ranging from 1/8 inch to1/4 inch. The expander tool 36 would have an outside diameter of about0.020 inches less than the inside diameter of the tube 13 with theprotrusions 28 having an effective outside diameter approximately 0.080inches larger than the inside diameter of the tube 13.

The tube 13 is preferably made of formable steel having a maximumhardness of R 40. The cams are preferably made of steel which ishardenable to a minimum hardness of R 58. Powder forged AISI 4660 seriesmaterial have also been successfully used as cams. The bearing rings arepreferably steels or iron compatible with the bushings. Also, powderedmetal rings have been used having an apparent hardness of R_(B) 90.

We claim:
 1. A method of making a camshaft having .[.cams and bearingrings.]. .Iadd.axially spaced members .Iaddend.on a rotatable tubecomprising the steps of:axially spacing and placing the .[.cams andbearing rings.]. .Iadd.axially spaced members .Iaddend.about therotatable tube, each .[.cam and each bearing ring.]. .Iadd.axiallyspaced member .Iaddend.having a cylindrical inside surface withcircumferentially spaced apart axially extending grooves on said insidesurfaces; axially aligning said grooves in said .[.cam and said bearingrings.]. .Iadd.axially spaced members .Iaddend.on said tube; andexpanding circumferentially spaced apart portions of the wall of thetube away from the tube axis and into the grooves on the inside surfacesof the .[.cams and bearing rings.]. .Iadd.axially spaced members.Iaddend.by axially inserting an expander tool having circumferentiallyseparated hard material protrusions constructed to expand portions ofthe wall of said tube away from the tube axis, into the tube, each ofsaid protrusions being positioned in axial alignment with each of saidgrooves so that as the protrusions move within the tube past the .[.camsand bearing rings.]. .Iadd.axially spaced members .Iaddend.the hardmaterial protrusions expand said portions of the wall into the grooveson the inside surfaces of the .[.cams and bearing rings.]. .Iadd.axiallyspaced members.Iaddend.. .Iadd.
 2. The method of claim 1, wherein saidaxially spaced members include cams. .Iaddend. .Iadd.3. The method ofclaim 1, wherein said axially spaced members include bearing rings..Iaddend.